The combination of the increasing size of the older adult population and the recent controversy over the administration of estrogen and progesterone to alleviate symptoms of menopause makes it imperative that we learn about the effects of gonadal steroids on cognition. The proposed research is based on a neurobiological model of the interaction of estrogen and the acetylcholine system and the effects of this interaction on normal cognition. Data indicate that estrogen attenuates the impairments on cognitive tests during anticholinergic drug challenge. Thus far, the role of progesterone in this model has not been elucidated. In order to understand the interaction of estrogen and progesterone with the cholinergic system, Study 1 will examine the performance of postmenopausal women who have taken these hormones for three months and then perform cognitive tests during anticholinergic drug challenges. Further, in an effort to learn about the brain circuitry affected by the hormones and anticholinergic drugs, Study 2 will involve drug challenge sessions conducted during functional magnetic resonance imaging. Thus, this research will provide knowledge about the interaction of gonadal steroids and the cholinergic system, the neuroanatomy of such interactions, and their influence on cognition in postmenopausal women.